Recent multimedia applications, such as wireless home audio and video applications, require sending or transmission of signals made of uncompressed video data over a communication network for display at a displaying device.
Today video data are often high-definition audio/video content, thus requiring communication at high data rate of several Gigabits per second (Gbps) with low latency and high quality of service for comfortable display.
For instance, an uncompressed high definition (HD) video (i.e., 60 Hz frames of 1920 vertical lines and 1080 horizontal lines corresponding to 1920×1080 pixels of 24 bits) has a bitrate of about 3 Gbps.
WPAN (standing for “Wireless Personal Area Network”) home networks based on millimetre wave unlicensed spectrum, referred to as 60 GHz millimetre wave technology, are suitable for home audio and video applications having such bitrate. Several standards of WPANs are currently in process, for example IEEE 802.11 Task Group, IEEE 802.15.3c standard, Wireless HD, WiGiG.
To offer a high level of reliability to the applications, the application data, i.e. the payload data generated by the application, are modulated into modulated symbols that have a higher bitrate than the payload data themselves, before they are converted into analogue signals and transmitted over the wireless medium (generally air) of the communication network.
The digital signal before conversion is made of raw data, the main part of which is made of the modulated symbols. Other raw data may be formed by headers, error-detecting codes, etc. The raw data thus represent the data as transmitted over the communication network.
Such higher bitrate may reach 50 Gbps and is due to the reliability mechanisms implemented in lowest layers of the OSI model (standing for “Open Systems Interconnection”), for example to the headers, to additional error-detecting codes, etc.
In this context, the lowest OSI layers of the communication devices must be designed to support very high rates.
The lowest OSI layer, so-called Physical (PHY) layer, is the layer which handles the data with the highest rate, and interfaces the communication device with the physical medium used for data transmission. Practically, the PHY layer implements modulator to modulate payload data received from the upper layer into modulated symbols and implements digital-to-analogue (D/A) converter to convert such modulated symbols into an analogue signal. Reciprocally, an analogue-to-digital, A/D, converter is implemented followed by a demodulator when operating in a receiving mode.
The next upper layer, so-called Data Link layer just above the PHY layer, provides the functional and procedural means to transfer data between communication devices of the network and to detect and possibly correct errors that may happen at the PHY Layer. A well-known sub-layer of the Data Link layer is the MAC layer (standing for “Media Access Control”).
Due to the complexity of the modulation/demodulation implemented at the PHY layer to provide high quality/high data rates wireless communications, the data rate used at the interface between the PHY layer and the communication module adapted to the wireless medium as well as the data rate used internally to the PHY layer are considerably higher than the data rate of the payload data provided by/to the Data Link layer.
For example, a ratio of ten is often observed between the highest data rate in the PHY layer and the payload data rate in the Data Link layer.
For cost reasons, the data path or interfacing link between the PHY layer and the Data Link layer is usually designed to support data rates of about the payload data rate, but not the highest data rates of the PHY layer. The maximum bandwidth of the interfacing link is designed to support at least the maximum payload data rate corresponding to the highest code rate implemented by the PHY layer and supported by the Data Link (or MAC) layer.
This interfacing link is generally a hardware link, such as for example a wire link with or without connectors, a chip-to-chip interface or an internal link inside an integrated circuit, because the PHY layer and the Data Link layer are often designed in separate hardware parts.
In particular, with high data rates, partitioning the communication device in two or more hardware parts may reveal to be advantageous.
For example, some applications would benefit a lot from integrating the PHY interface in a place very well adapted to communication but where space is too reduced to accommodate the entire device processing hardware.
In specific applications like radio communications where the power of received signal varies a lot with the position of the antenna (this is the case with 60 GHz radio communication systems), it is advantageous to freely integrate the PHY layer part everywhere in the device, independently of the application signal processing hardware.
The invention thus focuses on designs where a first hardware part implements essential means of the PHY layer, while a separate second hardware part implements at least essential means of the Data Link layer, including for example the MAC sub-layer and means for connecting to the application.
The two separate hardware parts can be two separate devices, two separate modules internal to the same device, two integrated circuits or two sub-parts on the same integrated circuit.
The link interfacing the two separate hardware parts is known as the MAC/PHY interface.
The invention also focuses on situations where non-demodulated data internal to the PHY layer are used by the Data Link or MAC layer. Non-demodulated data internal to the PHY layer encompass raw data directly retrieved from received digital signals and other data generated from such raw data, wherein the generation does not include demodulation.
This is to perform specific signal processing at the Data Link layer. For example, the PHY-layer non-demodulated data may help the Data Link layer to improve the communication quality.
In a case of point-to-point wireless communication, knowledge of received signals could be used to apply pre-coding in the communication device operating as a transmitter. For that case, raw data internal to the PHY layer could be transmitted to the Data Link layer, which in turn manages their transmission back to the transmitter in order for the transmitter to calculate and apply pre-coding of data.
This approach has been studied and corresponding results have been disclosed in publication “Writing on dirty paper with feedback” by Jialing Liut and Nicola Elia (Communications in information and systems, Vol. 5, N° 4, 2005).
Another case relates to channel measurements, like the Error vector Measurement (EVM), performed by the PHY layer that could be forwarded to the Data Link layer. This helps the latter to anticipate degradation of the communication quality and to set a new communication scheme if required (like a new relay scheme, new antenna settings).
Yet another case relates to signal measurement for chip calibration. In an example where the PHY layer is integrated on a chip and has analogue parts, A/D converters and digital signal processing unit, calibration of digital signal processing unit in the chip could be performed with regard to the behavior of the analogue parts integrated on the chip in factory.
These cases show that there are plenty of situations where non-demodulated data internal to the PHY layer are useful to an upper layer, in particular the Data Link layer.
As explained above, the interfacing link or MAC/PHY interface between the two layers is not designed to support transmission of all the non-demodulated data (about 50 Gbps). Solutions to overcome that situation are thus sought.
Publication U.S. Pat. No. 7,565,140 discloses a device for processing received wireless signals, wherein a network interface can be switched between two modes of operation. A first mode outputs signals having base-band values resulting from conversion of base band values of the received wireless signals using parameters such as a user-defined gain, a user-defined sampling frequency and a user-defined sampling rate. A second mode outputs signals having values representing data frames of the received wireless signals, based on conversion parameters according to a communication protocol.
The two modes of operation are exclusive one from the other, meaning that they cannot operate simultaneously.